The present invention relates to a system for recording signals on a recording medium using light beams, and likewise for converting recorded information into signals using light beams.
It has already been proposed to use a modulated laser beam to record signals on a recording medium of preferably disk-shaped configuration. This system makes possible a very high density of recorded information, but inherently requires very great mechanical precision, both in manufacture and in use, particularly for causing the beams to properly track information tracks on the recording medium. Additionally, this system is not suitable when, as in many practical applications, it is necessary to be able to simultaneously form two recording tracks which, because of the high information density involved, must be extremely closely spaced.
German published patent application DT-OS No. 2,341,571 discloses another system, in which a laser beam is split into two beams of mutually perpendicular polarization. These beams are then modulated in such a manner that one or the other of the beams can be used to record upon the recording medium, and in particular in such a way that they are alternately available for the recording of a bit in one or else the other of two tracks, respectively corresponding to logical "0" and "1" signals; the system in question does not have the capability of producing two tracks of recorded information simultaneously. Additionally, this known system has not solved important problems relating to automatic tracking, i.e., causing the modulated beam to accurately track the recording track upon which information is to be recorded.